Evaluating the impact of London’s Ultra-Low Emission Zone (ULEZ ) on physical activity and obesity in children


Air pollution exposure is associated with adverse health effects across the life-course. Children and adolescents are particularly vulnerable, with harms including increased risk of pre-term birth, pre-school wheeze, stunted lung growth, delayed cognitive development, new onset asthma, asthma attacks, and major mental health problems in adolescents.

Children’s Health in London and Luton (CHILL) is an NIHR-funded cohort study evaluating the impact of London’s Ultra Low Emission Zone (ULEZ) on children’s respiratory health. With additional funding from ARC North Thames and Barts Charity, we are adding outcomes, including physical activity and obesity, and cognitive development. 

This study builds on CHILL by collecting physical activity (by accelerometer) and travel patterns (by GPs) in the 3,300 children taking part. We test the hypothesis that a city-wide environmental intervention improving air quality and reducing traffic flows will improve children’s physical activity and reduce rates of obesity.

Key Findings

Early results show major improvements in air quality within the ULEZ, with children significantly more likely to switch to active travel (walking, scooting or cycling) to school, while those in Luton more often switched to travel by car. 

Among children who took inactive modes at baseline, 42% of children in London and 20% of children in Luton switched to active modes. For children taking active modes at baseline, 5% of children in London and 21% of children in Luton switched to inactive modes. Relative to the children in Luton, children in London were more likely to have switched from inactive to active modes (OR 4.69, 95% CI 1.82-12.05). Children in the intervention group were also less likely to switch from active to inactive modes (OR 0.22, 0.15-0.31). Moderator analyses showed that children living further from school were more likely to switch from inactive to active modes (OR 6.57,1.87-23.13) compared to those living closer (OR 1.52, 0.25-9.07).

These findings suggest that implementation of clean air zones can increase uptake of active travel to school and was particularly associated with more sustainable and active travel in children living further from school.

Partners & Collaborators

Queen Mary University of London

NIHR ARCs Yorkshire and Humber; South London; Northwest London; East of England

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